Vapor pressure relief system



Au 1, 1950 o. GARRETSON VAPOR PRESSURE RELIEF SYS'I'EI Filed lay 27,1946 INVENTOR.

O. L. GARRETSON ATTORNEYS 2 Patented Aug. 1, 1950 VAPOR PRESSURE RELIEFSYSTEM Owen L. Gar-retina, Bartleeville, rhilllpa Petroleum Company,Delaware Okla llllgnor to a corporation of Application Ray 27, 1948,Serial No. 672.600 1 Claim. (Cl. l37-53) This invention relates to vaporpressure relief systems. In one specific aspect it relates to vaporpressure relief systems for tanks containing a liquid of high vaporpressure in which the vapor pressure relief system is designed topreferentially draw vapor rather than liquid from the tank. In anotherspecific aspect, it relates to vapor pressure relief systems for tanksmounted on vehicles, which vehicles may be upset or overturned, but inwhich the vapor pressure relief system will still preferentiallydischarge vapor rather than liquid.

Liquids of high vapor pressure are often transported in vehicles. Suchvehicles are generally tank trucks and the liquid of high vapor pressureis often propane or butane or mixtures of the same or other hydrocarbonsof similar boiling point. Such tanks are provided with relief valves sothat when the pressure dllferential across the relief valve exceeds apredetermined amount, the relief valve will open and allow discharge offluid so that the tank will not burst. Due to such relief valves therehas been a minimum of danger connected with the transport of suchliquefied petroleum gases.

However, in a few instances the tank truck has been involved in anaccident with the result that the truck is displaced from an uprightposition. In the prior art, this has resulted in the relief valve beingconnected to the liquid in the tank instead of the vapor space above theliquid. As long as no fire occurs and the relief valve stays closed,there is no difliculty. In a few instances, there have been fires whichhave raised the vapor pressure inside the tank. The relief valve beingconnected to the liquid, because of the upset position of the tanktruck. the pressure generated by the fire is relieved by the venting ofliquid petroleum gas. The relief of liquid is not efficient in relievingvapor pressure above the liquid and the quantity of fuel discharged isgreatly increased because liquid is discharged. The liquid fueldischarged vaporizes and becomes ignited by the fire in most instancesin which case the fire already existing is greatly increased. which inturn raises the pressure and vents all the liquid.

The present invention provides means whereby the relief valve will onlydischarge vapor regardless of whether the tank truck is upside down ornot. Regardless of the truck position. both the liquid and thecounterweight on the pivoted inlet stack are in the lower region of thetank with the result that the relief valve can never discharge anythingbut vapor. or at least the discharge of liquid through said relief valveis minimized.

. One object of my invention is to provide an improved vapor reliefsystem for tanks containing liquids of high vapor pressure.

any discharge of liquid through such a vapor pressure relief system isminimized.

Another object is to provide automatic means for venting vapor andminimizing the discharge of liquid from a tank regardless of theposition in which the tank is disposed.

Another object is to provide a foolproof, simple and eillcientinstrumentality for carrying out the above objects.

Numerous other objects and advantages will be apparent to those skilledin the art upon reading the accompanying specification, drawings andclaim.

In the drawing:

Figure 1 is an elevational view of a liquid petroleum gas tank truckembodying the present invention.

Figure 2 is an enlarged cross sectional view, with parts broken away, ofa portion of Figure 1 showing in detail the vapor pressure reliefsystem.

In Figure 1, an automotive truck or other vehicle 3 is provided with atank 4 for containing liquid petroleum gas. Tank 4 may [be secured totruck 3 by any suitable means such as bands 5. Tank 4 is provided withrelief valve means for discharging fluid under excessive pressure to theatmosphere through stack 6. The outlet end of stack 6 may be closed byan easily removable rain cap I. The relief valve means is not shown inFigure 1, but will be described fully with reference to Figure 2.

In Figure 1, stack 6 and rain cap I are not absolutely essential as thefluid under excess pressure could be discharged from pipe I. It ispreferred to attach elbow 8 and stack 6, however, in order to direct thevapors upwardly to reduce chances of their ignition. Rain cap I iseasily blown out of pipe i by fluid pressure when the relief of pressureoccurs.

In Figure 2, tank 4 may be provided with an opening or man hole Ill andman hole It may be covered by a man hole cover ll secured to tank 4 bybolts I2 or other suitable means. In some aspects of the invention,however, the details of construction as to whether certain parts areintegral or separable or whether they detach at some point or another donot form any part of the invention as alternative construction willobviously operate in the same manner.

Man hole cover II has a relief valve opening 13 therethrough and securedto man hole It by welding I4 is the inlet end I! of a relief conduit.The relief conduit also comprises pipe 8, elbow 9 and stack i ifdesired, although parts i, I, I and 9 may be eliminated if desired.

Pipe I5 is secured in communication with opening l3 and pipe It has ananti-iriction-bearing swivel-Joint Ii mounted thereon. Because anyAnother object is to provide means whereby .0 suitable type ofswivel-Joint may be used at this 3 point, no details of construction areshown. Any usual ball bearing swivel-joint is preferred.

Rotatably mounted to swivel on swivel-joint I6 is a counterweightedstack generally designated as H. Stack I1 may consist of T l8, pipe 19,pipe 20, stack 2| (this having inlet opening 22 at its upper end) andcounterweight 23 is secured by welding 24 to pipe 20. Counterweight 23may contain lead 25 or suitable weighting material if necessary,depending on the ease with which swivel 16 operates.

Any of the usual types of relief valves may be inserted at any point inthe relief conduits 2|, l1, l9, I6, l5, II, 8, 9, or 6, but it ispreferable to place the relief valve so that it is relatively accessibleand yet not likely to be sheared off or otherwise removed from the tank4.

Therefore, I have located the relief valve generally designated as 26 atthe point shown. Relief valve 26 has a flange 21 on the exterior of itsbody '28 and this flange is secured to man hole cover H by means ofcollar 29 and bolts or other suitable fastening means 30.

Body 28 has a passage connecting the space inside pipe l to that insidepipe 3, and valve 26 has a valve head 3| normally urged to closedposition to close the passage in body 28 by spring 32 acting on valvestem 33. Valve stem 33 is connected with valve head 3 I. Valve head 3|may be provided with an eye 34 which eye is used in testing the reliefvalve. One form of construction which may be used for the connectionbetween spring 32 and valve stem 33 is the use of collar 35 and locknuts 36 and 31.

Operation The operation of the deviceis self evident. Should recklessdrivers in other vehicles force the driver of vehicle 3 off the highwayinto a ditch so that tank 4 is in an overturned position, and should thepressure in tank 4 (because of fire or for other reasons) become greatenough to open relief valve 26, the relief valve 26 will vent vapor tothe atmosphere, because stack 22 will have been rotated up into thevapor space above the liquid due to the action of the force of gravityon counter weight '25, as swivel 16 will allow such rotation.

The axis of rotation of swivel I6 is preferably parallel to thelongitudinal axis of truck 3 and, because of the relatively long wheelbase of truck 3, a swivel is sufficient at [6. If desired, swivel l6 maybe replaced by a suitable universal joint but, because of mechanicaldifliculties, a simple swivel I6 is preferable. Swivel-joint I6 ispreferably packed in the conventional manner to prevent any substantialamount of liquid from leaking from the tank into the relief conduit.

While I have shown in the drawing, a particular illustrative form of myinvention, various modifications may be made in the same and in thevarious features of construction, without materially changing theinvention therein, and formal changes may be made in the specificembodiment of the invention described without departing from the spiritor substance of the broad invention, the scope of which is commensuratewith the appended claim.

Having described my invention, I claim:

"In a tank for high vapor pressure fluids, the improvement of a pressurerelief device, comprising in combination a, single outlet conduitextending centrally through and rigidly affixed in a side wall of saidtank; a swivel flexibly attached and supported by the inner end of saidconduit and forming a passage therebetween; a stack rigidly attached tosaid swivel, communieating therewith, and extending upwardly therefromto a point above the normal liquid level in REFERENCES CITED Thefollowing references are of record in the file of this patent: V

UNITED STATES PATENTS Number Name Date 223,396 Shabley Jan. 6, 18801,365,567 Thomson Jan. 11, 1921 2,183,034 Voit Dec. 12, 1939 2,364,119Anderson Dec. 5, 1944

